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Re: [Qemu-ppc] [Qemu-devel] [PATCH for-2.9] pseries: Enforce homogeneous
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [Qemu-devel] [PATCH for-2.9] pseries: Enforce homogeneous threads-per-core |
Date: |
Sun, 2 Apr 2017 16:20:04 +1000 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Fri, Mar 31, 2017 at 11:04:55AM +0530, Bharata B Rao wrote:
> On Fri, Mar 31, 2017 at 10:21 AM, David Gibson <address@hidden>
> wrote:
>
> > For reasons that may be useful in future, CPU core objects, as used on the
> > pseries machine type have their own nr-threads property, potentially
> > allowing cores with different numbers of threads in the same system.
> >
>
> I remember we retained this flexibility to support heterogenous systems in
> future ? I think we can go with this enforcement now and relax it later if
> we ever reach there.
>
>
> >
> > If the user/management uses the values specified in query-hotpluggable-cpus
> > as they're expected to do, this will never matter in pratice. But that's
> > not actually enforced - it's possible to manually specify a core with
> > a different number of threads from that in -smp. That will confuse the
> > platform - most immediately, this can be used to create a CPU thread with
> > index above max_cpus which leads to an assertion failure in
> > spapr_cpu_core_realize().
> >
> > For now, enforce that all cores must have the same, standard, number of
> > threads. While we're at it, also enforce that the core ids are correctly
> > aligned based on that number of threads.
> >
> > Signed-off-by: David Gibson <address@hidden>
> > ---
> > hw/ppc/spapr_cpu_core.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > index 6883f09..935ee62 100644
> > --- a/hw/ppc/spapr_cpu_core.c
> > +++ b/hw/ppc/spapr_cpu_core.c
> > @@ -167,6 +167,18 @@ static void spapr_cpu_core_realize(DeviceState *dev,
> > Error **errp)
> > void *obj;
> > int i, j;
> >
> > + if (cc->nr_threads != smp_threads) {
> > + error_setg(errp,
> > + "Invalid nr-threads=%d of CPU[core-id: %d], must be
> > %d",
> > + cc->nr_threads, cc->core_id, smp_threads);
> > + return;
> > + }
> >
>
> The above check should move to pre_plug handler.
Ah, good point.
> > + if ((cc->core_id % smp_threads) != 0) {
> > + error_setg(errp, "Invalid CPU core-id=%d, must be a multiple of
> > %d",
> > + cc->core_id, smp_threads);
> > + return;
> > + }
> >
>
> Not sure when you will hit this as the same check is already present in
> pre_plug handler.
Oops, yes, didn't spot that.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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